1. Field of the Invention
The present invention relates to a glass flake, and further to resin compositions, paints, cosmetics, and ink compositions containing the glass flake.
2. Description of the Related Art
Glass flake is mixed in, for example, a resin matrix and improves the strength and dimensional accuracy of resin molded products. Glass flake is mixed in a paint as a lining material and applied onto surfaces of metals and concretes, and also is utilized in applications such as pigments and cosmetics.
Glass flake exhibits a metallic color when its surface is coated with a metal. It is also possible to provide glass flake with an interference color due to the interference of reflected light when the surface of the glass flake is coated with a metal oxide. The glass flakes on which a coating film of a metal or a metal oxide is formed are preferred for use in applications such as paints and cosmetics, in which color tones and gloss are seen as important. In the manufacturing step of coating the surface of glass flake with a metal or a metal oxide, the glass flake can be heated at high temperatures of 600° C. or higher after, for example, being coated by a liquid phase method.
As a composition suitable for glass flake, JP 63-201041A describes C glass, E glass, and a sheet glass composition. JP 2000-213639A describes a glass flake having good chemical durability. This glass flake has a glass composition that is free of diboron trioxide (B2O3) and fluorine (F), which are volatile components, and the content of alkali metal oxides is 5 mol % or less.
Glass flake can be fabricated with an apparatus shown in FIG. 1. In FIG. 1, a glass base 11 melted in a fire-resistant furnace bath 12 is inflated into a balloon-like shape by a gas that is supplied into a blow nozzle 15, forming a hollow glass film 16. The hollow glass film 16 is crushed by pressure rolls 17, forming a glass flake 1. The details of this apparatus are explained in, for example, JP 5-826A.
Taking the above-noted fabrication process into consideration, a glass flake is required to have good fusibility, appropriate temperature-viscosity characteristics, and a devitrification temperature lower than its working temperature. When the working temperature is too high, the glass flake becomes difficult to form; therefore, as for the temperature-viscosity characteristics of glass flake, a working temperature that is not exceedingly high, for example, a working temperature of 1300° C. or lower, is desirable.
Additionally, although not used in a glass flake, glass compositions that are free of diboron trioxide (B2O3), which is a volatile component, and have a small content of alkali metal oxides are known. JP 56-84336A describes a glass composition for sealing metal molybdenum. JP 1-126239A describes a glass substrate for electronic devices. JP 4-325435A describes a non-alkali glass. JP 5-232458A describes a glass for flat panel displays.
The present applicant has also proposed in JP 2000-247684A a glass composition that is free of ZnO, B2O3, and F2, for glass fibers.
Among the glass flake compositions described in JP 63-201041A, the C glass composition and the E glass composition require diboron trioxide (B2O3) and/or fluorine (F) as their essential components, in order to adjust the devitrification temperature and viscosity. These components tend to vaporize easily; therefore, they scatter around the surrounding area when melted, contaminating the work environment, and they corrode furnace walls of a smelting furnace and a regenerative furnace, reducing the life of the furnaces. Moreover, the so-called sheet glass composition (soda-lime composition) contains large amounts of alkali metal oxides. Therefore, the heat resistance performance is insufficient.
A glass flake composition described in JP 2001-213639A is a glass in which the total content of magnesium oxide (MgO), zinc oxide (ZnO), strontium oxide (SrO), and barium oxide (BaO) is 1≦(MgO+ZnO+SrO+BaO)≦10, that is, (MgO+SrO)≦10, expressed in mol %.
The glass composition disclosed in JP 2001-213639A contains zinc oxide (ZnO) or barium oxide (BaO) in many cases. However, zinc oxide (ZnO) easily vaporizes, and there has been a possibility that it may scatter around the surroundings when melted, contaminating the work environment. Moreover, another problem has been that because of the vaporization, the content in the glass is difficult to control. Therefore, it is preferable that zinc oxide (ZnO) not be used.
Moreover, in recent years, glass that does not use barium oxide (BaO) has been demanded due to considerations about the environment and human health. For this reason, it is preferable that barium oxide (BaO) not be used.
The glass shown as No.2 in Table 1 in JP 56-84336A contains a large amount of silicon dioxide (SiO2) at 62.2% in weight %, which is 70.0% when converted in mol %. The glass described in JP 1-126239A contains a large amount of aluminum oxide (Al2O3). The glasses described in JP 4-325435A and JP 5-232458A do not contain alkali metal oxides. For these reasons, all the glasses described in JP 56-84336A, JP 1-126239A, JP 4-325435A, and JP 5-232458A have high working temperatures, and glass flake is difficult to form.
All the Examples in JP 56-84336A contain barium oxide (BaO). All the Examples in JP 4-325435A contain boron trioxide (B2O3).
All the Examples in JP 1-126239A have a working temperature of 1399° C. or higher.